rebuilding a 727 to hold a 600 hp motor

Except for installing a bolt in rear sprague it doesn't take anything other than a rebuild with good parts and includes setting all the clearances correctly. A very good book on 727's is by Carl Munroe and is about $20 on Amazon. It goes into detail describing how the 727 works and how to rebuild it for a stock engine all the way to a full race unit. Go to Amazon and type in 727 torqueflite and it'll come up